Field of the Invention
Embodiments of the present invention relate to apparatuses, systems, devices, and methods for wireless communication with one or more remote devices that reduce or eliminate interference from zero-mean noise and deterministic signals within the system operating frequency band. The apparatuses, systems, devices, and methods are particularly advantageous when used to extract identification and/or sensor data from passive wireless sensors and tags, including those that respond with differential responses at specific delays such as from sets of surface acoustic wave (SAW) based sensor tag devices. In particular, embodiments of the present invention relate to improved methods for implementing an interrogator for said remote devices that uses dithering of the initiation time of sequential transmitted signals, along with synchronous accumulation of the resulting received signals, to cause the interfering signals to be reduced in relative size while increasing the relative strength of the desired signal.
Description of Related Art
Acoustic Wave Sensors: Sensors based on surface-launched acoustic wave devices have been developed since the 1980's for application to physical measurements (temperature, pressure, torque, strain, etc.) and to a wide range of chemical and biological detection problems. These widely varying devices have been described in detail in the open literature, including the following: U.S. Pat. No. 7,268,662, entitled Passive SAW-based hydrogen sensor and system, U.S. Pat. No. 7,434,989, entitled SAW temperature sensor and system, U.S. Pat. No. 7,500,379, entitled Acoustic wave array chemical and biological sensor U.S. Pat. No. 7,791,249, entitled Frequency coded sensors incorporating tapers, U.S. Pat. No. 8,094,008, entitled Coded acoustic wave sensors using time diversity, U.S. Pat. No. 8,441,168, entitled SAW Sensor tags with enhanced performance, U.S. Pat. No. 9,121,754, entitled Surface Acoustic Wave Deposition Monitor for Ultra-Thin Films, U.S. Utility application Ser. No. 13/679,607 (US20130130362A1), entitled Power Spectral Density Chemical and Biological Sensor, and U.S. Utility application Ser. No. 13/694,889 (US20130181573A1), entitled Individually Identifiable Surface Acoustic Wave Sensors, Tags, and Systems.
Acoustic Wave Sensor Interrogation Systems: Acoustic wave sensor devices have been operated within a wide range of wired and wireless interrogation system architectures, which have generally been designed specifically to operate with the selected sensor(s). The system architecture is usually selected based on specific device characteristics and application requirements, and generally involves absolute or differential measurements of sensor frequency, phase, delay, amplitude, or power spectral density, and changes in these quantities with exposure to changes in target parameters, to provide the output sensor measurement.
Conventional wireless interrogation system architectures include pulsed radar-like delay measurement systems, Fourier transform based measurement systems, delay line and resonator-based oscillator systems, and time-integrating correlator based interrogation systems. Radio architectures include conventional homodyne and heterodyne mix-down systems, and direct (to baseband or to near-baseband) conversion systems. A typical down-mixed correlation based radio receiver that uses coherent integration of multiple sweeps to increase signal to noise ratio (S/N) is described by Kozlovski et. al., “A 915 MHz SAW Correlator System,” IEEE Sensors Journal, Vol. 11, No. 12, December 2011, pp. 3426-3432. This synchronous correlator approach is implemented in a down-mixed software defined radio (SDR) system by Humphries and Malocha, “Software Defined Radio for Passive Sensor Interrogation,” Proceedings of the 2013 IEEE Joint UFFC, EFTF, and PFM Symposium, 2013, pp. 270-273. Humphries describes modifying a commercially available software defined radio in order to provide for synchronous data accumulation.
Dithering in radar systems and sampled data: Analog-to-digital (A/D) converters (ADCs) have been widely used in electronic systems ranging from military radar to audio and image processing. The process of A/D conversion produces quantization noise, which is often correlated and can produce spectral harmonics that degrade the digitized signal, introducing significant distortion particularly when the signal is small (on the order of the quantization step). As discussed by Thakur et. al., “Utilization of Noise to Enhance the Performance of Radar Signal Processor,” 9th International Radar Symposium India, 2013, adding noise to the signal prior to quantization can randomize the ADC quantization noise, improving overall system performance. This effect has been studied extensively since the early 1960's, and is widely used to provide enhanced system performance for audio systems, image processing, radar, direct down conversion receivers, and numerous other systems. Dithering techniques include addition of noise like signals to the received signal prior to A/D conversion, with the added signal either subtracted out of the digitized signal (subtractive) or not subtracted out (non-subtractive). Additional techniques discussed as dithering in the context of radar electronic counter counter measures (ECCM) include modification of the system transmit properties such as frequency hopping and bandwidth hopping.